JPH0448433A - Binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain uniform dispersion of fine particles of magnetic powder by constituting the binder from specified amts. of vinyl chloride, hydroxy group- contg. vinyl, N-substd. maleimide and amino group-contg. polymerizable monomers. CONSTITUTION:The amt. of vinyl chloride is 59 - 98 wt.%, which is decided by the following reason. If the amt. is small, solubility of the binder to an org. solvent decreases, while with large amt. the obtd. copolymer has low flexibility. The amt. of hydroxy group-contg. vinyl structural unit is 1 - 30 wt.%. If the amt. is smaller, dispersibility of the magnetic powder in vinyl vhloride copolymers decreases, while with larger amt., solubility to an org. solvent decreases. The amt. of N-substd. maleimide is 1 - 40 wt.%. With smaller amt., dispersibility of the magnetic power, heat resistance of copolymers and wearing resistance of the magnetic layer decrease, while with larger amt., the obtd. layer becomes brittle. The amt. of amino group-contg. polymerizable monomers is 0.05 - 5 wt.%. With smaller amt., dispersibility of the magnetic powder decreases, while with larger amt., surface smoothness and moisture resistance of the layer decrease. Thereby, fine particles of the magnetic powder can be uniformly dispersed.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a binder for magnetic recording media.

(Prior art) Generally, magnetic recording materials used for magnetic tapes, magnetic disks, etc. are produced by applying a magnetic paint containing magnetic powder and a binder onto a base material, applying a magnetic field to orient the magnetic powder, and then It is produced by forming a magnetic layer by drying, but in order to obtain a magnetic recording body with excellent magnetic properties, it is necessary to uniformly disperse the magnetic powder in the binder. Conventionally, vinyl chloride-vinyl acetate-vinyl alcohol polymers, mixtures of these polymers and isocyanate compounds, and the like have been known as the above-mentioned binders.
No. 04 proposes a vinyl chloride copolymer consisting of vinyl chloride and 2-hydroxypropyl acrylate as a binder capable of dispersing WA-free pigments well.

However, in recent years, magnetic powder has been made into finer particles as the density of magnetic recording bodies has increased, and the above-mentioned binder has been insufficient in dispersibility of the finely divided magnetic powder. Furthermore, the durability of sliding contact with the magnetic head was also insufficient.

(Problem B to be Solved by the Invention) The present invention has been made in view of the above drawbacks, and it is possible to form a magnetic layer in which finely divided magnetic powder is uniformly dispersed and has excellent magnetic properties. An object of the present invention is to provide a binder for magnetic recording bodies.

(Means for Solving the Problems) The binder for a magnetic recording medium of the present invention is composed of a vinyl chloride constitutional unit, a hydroxyl group-containing vinyl constitutional unit, an N-substituted maleimide constitutional unit, and an amino group-containing polymerizable monomer constitutional unit. It consists of a vinyl chloride copolymer.

The hydroxyl group-containing vinyl forming the above-mentioned hydroxyl group-containing vinyl structural unit is not particularly limited as long as it has a reactive double bond and a hydroxyl group, and examples thereof include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (
meth)acrylate, 3-chloro-2-hydroxypropyl(meth)acrylate, polyethylene glycol mono(meth)acrylate represented by formula (1) (n is 2
an integer of ~9, R is hydrogen or methyl group), CH, ・CR-Co(CH2-CHz-O)-, lHl
-(11 (2) Polypropylene glycol mono (
meth)acrylate (n is an integer of 2 to 6, R' is hydrogen or methyl group), reaction product of (meth)acrylic acid ester and polyhydric alcohol such as 2-hydroxyethyl-2-acryloyloxyphthalate, N-methylol Examples include (meth)acrylic acid amides such as (meth)acrylamide, and 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are preferably used.

The N-substituted maleimide forming the N-substituted maleimide structural unit is a compound represented by general formula (3).

In the formula, R2 is not particularly limited as long as it is an aliphatic group, an alicyclic group, or an aromatic group having 1 to 20 carbon atoms, and includes, for example, N-methylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide. , N-n-butylmaleimide, N-tert-butylmaleimide, N-n-hexylmaleimide 1', N-cyclohexylmaleimide, N
-phenylmaleimide, N-2-chlorophenylmaleimide, N-2-methylphenylmaleimide, N2-ethylphenylmaleimide, N-2,6-cyclohexylmaleimide, N-2,6-dimethylphenylmaleimide,
N-hensylmaleimide, N-(2-chlorobenzyl)
Maleimide, N(2-methylhensyl)maleimide, N
-naphthylmaleimide, etc., and N-cyclohexylmaleimide and hephenylmaleimide are preferably used.

The amino group-containing polymerizable monomer forming the amino group-containing polymerizable monomer constitutional unit is not particularly limited, and examples thereof include dimethylamino (meth)acrylate, diethylamino (meth)acrylate, N, N -dimethylaminopropylacrylamide, tert-butylaminoethyl (meth)acrylate, and the like.

If the amount of the vinyl chloride structural unit is small, the solubility in solvents will decrease, and if it is large, the vinyl chloride copolymer will become hard and its flexibility will decrease.
If the amount of the hydroxyl group-containing vinyl structural unit decreases, the dispersibility of the magnetic powder in the vinyl chloride copolymer will decrease, and if it increases, the solubility in organic solvents will decrease, so it should be 1 to 30% by weight. However, when the amount of the N-substituted maleimide structural unit decreases, the dispersibility of the magnetic powder in the vinyl chloride copolymer, the heat resistance of the vinyl chloride copolymer, and the abrasion resistance of the magnetic layer decrease. If the amount of the amino group-containing polymerizable monomer is small, the dispersibility of the magnetic powder in the vinyl chloride copolymer will decrease, and the amount of the amino group-containing polymerizable monomer should be 1 to 40% by weight. If this happens, the surface smoothness and moisture resistance of the magnetic layer will deteriorate, so the content should be 0.05 to 5% by weight.

When the average degree of polymerization of the vinyl chloride copolymer constituting the binding side for the magnetic recording body of the present invention becomes small, the mechanical strength of the magnetic layer decreases, and when it becomes large, the mechanical strength decreases! It is preferably 150 to 800 because the viscosity of the solution when dissolved in a solvent becomes too high and the dispersibility of the magnetic powder and the moldability of the magnetic layer decrease.

Any method may be adopted as the method for producing the above-mentioned vinyl chloride copolymer, such as the known suspension polymerization method which is usually carried out in the polymerization of vinyl chloride using a radical polymerization initiator;
Examples include emulsion polymerization method, solution polymerization method, and bulk polymerization method.

The suspension polymerization method does not contain impurities in the resulting polymer.
, and is preferably adopted because the manufacturing cost is relatively low.

In the above suspension polymerization method, the suspension stabilizer is not particularly limited, and for example, partially saponified polyvinyl alcohol, cellulose derivatives, etc. may be used, and the radical polymerization initiator is not particularly limited, such as ,
Organic peroxides such as hensyl peroxide, dilauroyl peroxide, and tert-butyl peroxyneodecanoate are used. The N-substituted maleimide is
The entire amount may be added into the polymerization vessel at once before the start of polymerization, the entire amount may be added in portions during polymerization, or it may be added continuously.

In particular, N whose copolymerizability ratio with vinyl chloride is significantly different
- When using an N-substituted maleimide such as phenylmaleimide, it is preferable to add the entire amount in portions during polymerization or to add it continuously as this will further improve heat resistance. In this case, N-substituted maleimide is acetone,
It is preferable to use it by dissolving it in an organic solvent such as methanol or by dispersing it in water.

The composition of the binder for a magnetic recording medium of the present invention is as described above, and it can be copolymerized with vinyl chloride within a range that does not reduce the basic performance as a binder such as the dispersibility of magnetic powder and heat resistance. Monomers may be copolymerized, and the content is 10% by weight
The following are preferred.

The above monomer is not particularly limited, but
For example, α-olefins such as ethylene and propylene, vinyl esters such as vinyl acetate and vinyl propionate,
Vinyl ethers such as butyl vinyl ether and cetyl vinyl ether, acrylic acid esters such as methyl acrylate and ethyl acrylate, methyl methacrylate,
Methacrylic acid esters such as ethyl methacrylate and phenyl methacrylate, aromatic vinyls such as styrene and α-methylstyrene, vinyl cyanides such as acrylonitrile and methacrylonitrile, vinyl halides such as vinylidene chloride and vinyl fluoride, and malein. Examples include unsaturated dicarboxylic acid esters such as dimethyl acid and dimethyl fumarate, and unsaturated dicarboxylic acid anhydrides such as maleic anhydride.

Further, a polymerizable monomer containing a functional group other than an amino group that can be copolymerized with vinyl chloride may be further copolymerized within a range that does not reduce the basic performance of the binder for magnetic recording material of the present invention. Generally, its content is preferably 5% by weight.

The above polymerizable monomer is not particularly limited, but examples include acrylic acid, maleic acid, maleic acid n
- Carvone Ml such as butyl monoester! , 2-acrylamide-2-methylbrobanesulfonamide,
Polymerizable monomers containing sulfonic acid groups or sulfonic acid groups such as sodium metaallyl sulfonate, polymerizable monomers containing phosphoric acid groups such as acid phosphoxyethyl (meth)acrylate, acid phosphoquinpropyl (meth)acrylate, etc. Examples include polymerizable monomers containing quaternary ammonium bases such as 2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride and methacryloyloxyethyltrimethylammonium chloride.

A method for producing a magnetic paint from the binder for magnetic recording material of the present invention may be any known method. For example, cobalt-T-iron oxide or the like is added to a solution in which the binder is dissolved in an organic solvent. One example is a method of dispersing magnetic powder.

The content of the binder and magnetic powder in the magnetic paint may be determined as appropriate depending on the conditions for forming the magnetic layer obtained by applying and drying the magnetic paint. The content of the binder is preferably 5 to 30% by weight, and the amount of binder added to the magnetic powder is 10 to 1 part by weight per 100 parts by weight of the magnetic powder.
00 parts by weight is preferred.

Examples of the organic solvent include, but are not limited to, toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like.

Further, in order to improve the abrasion resistance and heat resistance of the magnetic layer, an isocyanate compound may be added to the magnetic coating material.

The above-mentioned isocyanate compound is not particularly limited, but examples include tolylene diisocyanate, diphenylmethane diisocyanate, dianisidine diisocyanate, hexamethylene diisocyanate, metaxylylene diisocyanate, and a reaction product of trimethylolpropane and tolylene diisocyanate. etc. can be mentioned. If the amount of the isocyanate compound added is too small, it will not be possible to improve the abrasion resistance, heat resistance, etc. of the magnetic layer, and if it is too large, the crosslinking density will increase and the magnetic layer will become brittle. It is preferably 0.3 to 30 parts by weight.

(Example) The present invention will be explained in detail below.

The methods for measuring the degree of polymerization and composition of the vinyl chloride copolymer and the physical properties of the magnetic recording medium shown in the results are as follows.

fil degree of polymerization Measured in accordance with JIS K6721.

(2) Composition After measuring the chlorine content by the oxygen flask combustion method, the component composition was determined using an elemental analysis bag W (manufactured by Yanagimoto Seisakusho Co., Ltd., model i CHN coder MT-5).

(3) Glossiness digital variable angle glossy needle (manufactured by Nihon Heavy Industries, model: VG-
IC).

(4) The base films on which the heat-adhesive magnetic layers have been formed are stacked so that the magnetic layer surfaces are in contact with each other, and after heating at 120°C for 15 minutes with a load of 70 g/aJ applied, one edge of the film is heated. 01 when both films peeled off when lifted.
Those that remained adhered were rated as ×.

(5) A sample for gel fraction measurement was immersed in a mixed solvent of toluene-methyl isobutyl ketone (weight ratio 1/1) at 50°C for a day and night, and the undissolved content expressed as a weight percentage of the sample was determined as the gel fraction. did.

In addition, as a sample for measurement, a composition obtained by removing magnetic powder from the magnetic paint obtained in each example was applied onto a glass plate.
The material formed by drying at 00°C for 2 hours and further at 50°C for 24 hours was used.

(6) Square ratio DC magnetization characteristic recording device (Yokogawa Electric Corporation, model iT/32
56-30).

8 kg of ion-exchanged water, 1 g of hydroxypropylethyl cellulose, and 8.8 g of dilauroyl peroxide were charged into a pressure-resistant polymerization vessel equipped with a jacket and equipped with a stirrer, and the vessel was sealed to remove residual air. 3 kg was press-fitted and then heated to 70°C using a salmon 7). Immediately after the internal temperature reaches 70°C, add 10 g of 2-hydroxypropyl acrylate, 7 g of N-cyclohexylmaleimide, and 1 g of diethylaminoacrylate.
A solution prepared by dissolving Log in acetone was added in an amount of one batch, and the solution was injected 40 times at 5 minute intervals, and polymerization was carried out with stirring. After the final addition, the mixture was cooled for 5 minutes, and after cooling, the remaining unreacted vinyl chloride was discharged outside the vessel. Next, the polymerization slurry was taken out, washed with ion-exchanged water, and dried to obtain a vinyl chloride-based copolymer. Ta.

The degree of polymerization and composition of the obtained copolymer were measured and the results are shown in Table 1.

Next, the obtained copolymer was dissolved in a mixed solvent of toluene-methyl isobutyl ketone (weight ratio 1/1) to prepare a 15% by weight copolymer solution, and the resulting solution was 4 times that of the copolymer. A weight of cobalt γ-iron oxide was supplied to a paint conditioner equipped with a 1/8 inch stainless steel pole, and the mixture was partially dispersed for 4 hours to obtain a magnetic paint.

The obtained magnetic paint was applied to a polyethylene terephthalate film with a thickness of 25 μm, and a magnetic field with a magnetic flux density of 2000 GS was applied to orient the magnetic powder, and then dried to form a magnetic layer with a thickness of 6 μm. A magnetic recording medium was obtained.

The squareness ratio and glossiness of the surface of the magnetic layer of the obtained magnetic recording body were measured, and the results are shown in Table 1.

As shown in Table 1, a copolymer obtained in the same manner as in Example 1 was used except that the type and amount of the composition in the copolymer was changed. A magnetic recording medium was obtained in the same manner.

The composition and degree of polymerization of the obtained copolymer and the physical properties of the magnetic recording material were measured in the same manner as in Example 1, and the results are shown in Table 1.

As shown in Table 1, a copolymer obtained in the same manner as in Example 1 was used except that the type and amount of the composition in the copolymer was changed. A magnetic recording medium was obtained in the same manner.

The composition and degree of polymerization of the obtained copolymer and the physical properties of the magnetic recording material were measured in the same manner as in Example 1, and the results are shown in Table 1.

A magnetic recording material was obtained in the same manner as in Example 1, using vinyl chloride-vinyl acetate-vinyl alcohol copolymer as the copolymer.

The physical properties of the obtained magnetic recording body were measured in the same manner as in Example 1, and the results are shown in Table 1.

(Left below) The magnetic paint obtained in Example 1 was coated with an isocyanate compound (
Manufactured by Nippon Polyurethane Co., Ltd., product name: Coronet, solid content 7
A magnetic recording material was obtained in the same manner as in Example 1, except that 3 parts by weight of 0% by weight) were added to 100 parts by weight of the copolymer and mixed to prepare a magnetic coating material. The squareness ratio, glossiness, heat adhesion, and gel fraction of the obtained magnetic recording material were measured, and the results were reported in the second
Shown in the table.

Example 7 using each of the magnetic paints obtained in Examples 2 to 6.
A magnetic recording medium was obtained in the same manner as above. Measure the squareness ratio, glossiness, heat adhesion, and gel fraction of the obtained magnetic recording material,
The results are shown in Table 2.

Comparative Group 1 Using the magnetic paint obtained in Comparative Example 3, a magnetic recording medium was obtained in the same manner as in Example 7. The squareness ratio, glossiness, heat adhesion and gel fraction of the obtained magnetic recording body were measured, and the results are shown in Table 2.

Table 2

Claims (1)

[Claims] 1. 59-98% by weight of vinyl chloride structural units, 1-30% by weight of hydroxyl group-containing vinyl structural units, 1-40% by weight of N-substituted maleimide structural units, and 0.05-5% of amino group-containing polymerizable monomer structural units. Binder for magnetic recording material consisting of % by weight.